1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly, to an actuator that moves a magnetic head to record and to reproduce data to a predetermined position on a disk, and a hard disk drive employing the same.
2. Description of the Related Art
Hard disk drives (HDDs) are auxiliary storage devices used with a computer. The hard disk drive reads out data stored on a magnetic disk or record data on the magnetic disk by using a magnetic head.
FIG. 1 is a perspective view illustrating a conventional hard disk drive. Referring to FIG. 1, the conventional hard disk drive includes a housing 10, a magnetic disk (hard disk) 20 that is a recording medium included in the housing 10, a spindle motor 30 included on a base plate 11 of the housing 10 to rotate the disk 20, and an actuator 40 having a magnetic head (not shown) to record and reproduce data.
The housing 10 is included inside a main body of a computer and includes the base plate 11 supporting the spindle motor 30 and the actuator 40 and a cover plate 12 coupled to the upper portion of the base plate 11 and encompassing and protecting the disk 20.
The disk 20 is a recording medium to record data and one or a plurality of disks are included in the computer and are to be separated a predetermined distance from each other and are capable of being rotated by the spindle motor 30. A parking zone 21 where a slider 42 where the magnetic head is mounted when the power is turned off is included at the inner circumferential side of the disk 20. A data zone 22 where data is stored is included outside the parking zone 21.
The actuator 40 includes an arm 46 included to pivot around a pivot shaft 47 included on the base plate 11, the slider 42, and a suspension 44 included at an end portion of the arm 46 and supporting the slider 42 to be elastically biased toward a surface of the disk 20. The arm 46 is rotated by a voice coil motor 50. A lower yoke 51 is fixedly included on the base plate 11. An upper yoke 52 is coupled above the lower yoke 51.
In the conventional hard disk drive having the above structure, during which data is being recorded/reproduced, a lifting force by the rotation of the disk 20 and an elastic force by the suspension 44 are applied to the slider 42. Accordingly, since the slider 42 is lifted and remains in a lifted state above the data zone 22 of the disk 20 at a height where the lifting force and the elastic force are balanced, the magnetic head mounted on the slider 42 maintains a predetermined distance from the disk 20 that is rotating to record or reproduce data with respect to the disk 20. When the power is turned off and the disk 20 stops rotating, since the lifting force lifting the slider 42 disappears, the slider 42 must be moved from the data zone 22 of the disk 20 in advance. That is, as the arm 46 of the actuator 40 is moved by the voice coil motor 50 so that the slider 42 is moved to the parking zone 21 of the disk 20 before the disk 20 stops rotating completely, even when the rotation of the disk 20 is stopped, the slider 42 is disposed in the parking zone 21 so that damage done to the data zone 22 is prevented. When the power is turned on and the disk 20 resumes rotating, the lifting force is generated again and accordingly the slider 42 is lifted. Then, the slider 42, while lifted, is moved to the data zone 22 of the disk 20 as the arm 46 is rotated by the voice coil motor 50. The magnetic head mounted on the slider 42 records or reproduces data with respect to the data zone 22 of the disk 20.
FIG. 2 shows a perspective view illustrating a conventional actuator. Referring to FIG. 2, the conventional actuator 40 includes the arm 46. A pivot hole 48 is formed in the middle of the arm 46 and the pivot shaft 47 shown in FIG. 1 is inserted into the pivot hole 48. The suspension 44 is included at an end portion of the arm 46 and supporting the slider 42 where a magnetic head 41 is mounted to be elastically biased toward a surface of the disk 20. A coil 56 of the voice coil motor 50 is coupled to the rear end portion of the arm 46. Magnets 53 and 54 of the voice coil motor 50 are included at lower and upper sides of the coil 56, respectively, to face each other with a predetermined interval therebetween. The magnets 53 and 54 are attached to the upper surface of the lower yoke 51 of FIG. 1 and the lower surface of the upper yoke 52 of FIG. 1, respectively.
The coil 56 is coupled to the arm 46 by a plastic injection molding. That is, plastic resin is injection molded to form an outer mold 49a outside the coil 56 and an inner mold 49b inside the coil 56. Accordingly, the coil 56 is fixedly coupled to the rear end portion of the arm 46 by coupling forces between the outer circumferential surface of the coil 56 and the outer mold 49a, and the inner circumferential surface of the coil 56 and the inner mold 49b. 
The actuator 40 having the above structure is controlled by a servo control system and moved in a direction according to the Fleming's left hand rule by the interaction between current applied to the coil 56 and the magnetic field generated by the magnets 53 and 54. Here, the rotation direction of the actuator 40 changes rapidly according to the direction of the current applied to the coil 56 by the servo control system. The movement speed of the magnetic head 41 is an important factor in determining seek time of a hard disk drive. Thus, it is advantageous to generate a strong force (torque).
During the operation of the hard disk drive, the actuator 40 repeatedly changes a pivot direction instantly to move the magnetic head 41 to a desired place. Such movements generate vibrations having a variety of frequencies and amplitudes in the actuator 40 and the vibrations cause the magnetic head 41 to vibrate. When the magnetic head 41 vibrates, a position error signal (PES) increases which will impede the read/write function of the magnetic head 41 along a track formed on the disk. Thus, since the performance of the hard disk drive can be improved by minimizing the vibrations, the dynamic characteristic of the respective part of the actuator 40 should be optimally designed and the parts should be firmly coupled to one another.
However, in the conventional actuator 40, in the process of plastic injection molding to couple the coil 56 to the rear end portion of the arm 46, the coupling force between the inner mold 49b and the coil 56 can be deteriorated due to contraction of the inner mold 49b. More particularly, as plastic resin is cooled, the plastic resin contracts so that the coupling force between the outer mold 49a and the coil 56 increases while the coupling force between the inner mold 49b and the coil 56 decreases. In this state, when vibrations are generated in the actuator 40, the inner mold 49b and the coil 56 may be partially separated. Accordingly, the dynamic characteristic of the system deteriorates and the vibration of the actuator 40 increases, thus the performance of the magnetic head 41 deteriorates. Also, if the coupling state between the coil 56 and the arm 46 is inferior, the resonance frequency of the actuator 40 is lowered. Accordingly, when the resonance frequency is lowered and deviated from a range in which the servo control system can control, the normal operation of the actuator 40 is not possible.
FIG. 3 is a graph showing the amplitude of a magnetic head portion according to the frequency in the conventional actuator. Referring to the graph of FIG. 3, a peak value of the amplitude is high in a high frequency area A. As shown in the graph of FIG. 3, if the coupling state between the coil and the arm is inferior, the dynamic characteristic of the system is deteriorated which will degrade the quality of a product. Furthermore, when the deviation in the quality of mass produced products increases, consistent quality of the products cannot be expected.